1. Field of the Invention
This invention relates to a solid treatment composition and method for treating water systems for scale, biofilm and microbial growth, and corrosion. This invention is particularly useful in anthropogenic cooling and chilled water applications, such as cooling towers, and boiler systems.
2. Description of Related Art
Anthropogenic water systems are critical components commonly found in most of the world's energy producing facilities, industrial and manufacturing plants, hospitals, and other institutional complexes and buildings. These systems consume around 700 billion gallons of water annually with a cost of $1.8 billion in sewage handling costs alone. All of these anthropogenic water systems require some form of treatment, either chemical or non-chemical, to control the build-up of scale, biofilm and other corrosion by-products on the important heat transfer surfaces that are necessary for efficient system operation.
For water systems involving heat exchange, such as cooling towers and boilers, effective treatment to remove these contaminants and to prolong the amount of time before the systems are re-contaminated can save significant amounts of money. An effective and thorough treatment may save costs for labor and treatment chemicals by reducing the frequency of periodic treatments or reducing the amount of chemicals needed for routine maintenance and/or periodic treatments. Such a treatment may also save on energy costs through the operation of clean heat exchange surfaces. Fouling of heat exchange surfaces costs U.S. industry hundreds of millions of dollars every year and is directly related to an increase in energy consumption of almost 3 quadrillion Btus (quads) annually.
To maximize the water usage and minimize waste, many of these systems employ a series of chemical treatments that protect the system against scaling, biofilm formation, and corrosion. For example the Chem-Aqua 15000 MTP product is one of the most common cooling tower chemical treatments, containing 2-phosphonobutane-1,2,4-tricarboxylic acid, and a series of high performance polymers to prevent calcium carbonate scale formation, azoles to inhibit copper corrosion and small amounts of molybdate for trace analysis. Chemical treatments such as the Chem-Aqua 15000 MTP product may be used with a number of non-oxidizing biocides including Bacticide 45 which is a 45% gluteraldehyde solution, Coolicide which is a 15% poly-quaternary ammonium solution, or a 1.5% Isothiazolin solution. In the larger industrial cooling tower systems and the cooling towers for coal and nuclear facilities it is more common to use sodium hypochlorite, 40% sodium bromide, or 11% bromine chloride liquid as the disinfectants.
These chemical treatments allow the water to be reused and recycled a number of times before it becomes necessary to discharge the water and replace it with fresh water. Increasing the duration for which the water may be circulated significantly reduces the amount of water that is discharged to the sewage system and minimizes the amount of make-up water that is needed to replace the bleed off. The chemical treatments also maintain the efficiency of the cooling tower and heat exchanger system. Many prior art treatment compositions and methods involve the use of liquid chemicals, typically shipped in large drums, which may make shipping and handling of the chemical compositions more difficult and expensive. Liquid treatments may be concentrated to reduce the volume of treatment product that must be shipped; however, the ingredients that may be useful in such treatment products are often not compatible in a concentrated liquid form, which limits the ability to use concentrated liquids. For example, certain surfactants, such as SugaQuats, will precipitate from solution rendering a concentrated liquid mixture inactive. Additionally, shipping and handling concentrated liquid treatment compositions can still be more costly and hazardous than if the treatment composition were in a solid form.
Additionally, many prior art treatment compositions and methods may damage the components of the water system being treated as the chemicals used are highly corrosive. There is also an environmental down side to the treatments. It is estimated that there are 536 billion pounds of water treatment chemicals discharged as a result of cooling tower treatments every year, which may impact a variety of species living in or near areas and water-ways receiving the discharge. Therefore it is desirable to use treatment chemicals that are considered less toxic. For example, citric acid and sodium citrate, which are both approved food additives, have been used in treatment compositions. The use of citric acid and sodium citrate, along with a cationic surfactant, is disclosed in Applicant's co-pending U.S. patent application Ser. No. 13/837,256.
Many prior art treatment compositions and methods require the use of strongly acidic, oxidizing, and toxic biocides for removal of biofilms. Biofilms contain mixed communities of bacteria including various species embedded in an exopolymer or “slime layer.” As bacteria begin to attach to a surface, they secrete polymers, such as polysaccharides and glycoproteins called fibronectin. These allow the bacteria to adhere to a surface and form the conditioning layer of the biofilm. Once a confluent surface of sessile cells has formed, any other bacteria that contact this layer will be captured. Thus bound in this way, these bacterial cells begin to produce anchoring organelles and other compounds, allowing a secondary layer to form on top of the conditioning layer. As cells continue to attach and accumulate, underlying layers continue to reproduce and create a dense bacterial cluster. As these biofilm layers form they also accumulate other inorganic and organic debris that grow within the pipe restricting flow and causing blockages.